Move from a hacky direnv cache to nix-direnv plugin

I've been using a hacked up caching speedup of direnv for a while now:
https://gist.github.com/zimbatm/77bfa0268b5a2a540c4d0d9189bb1ae2

But now I've realized that a similar approach has been released as a proper
plugin and is available in 20.03 nixpkgs, so this commit removes the old
hack and replaces it with the shiny new `nix-direnv` plugin.

More info on https://github.com/nix-community/nix-direnv/

Also, had to update to latest 20.03 nixpkgs to be able to install `nix-direnv`.

.direnvrc

@@ -0,0 +1,3 @@
+if [ -f /run/current-system/sw/share/nix-direnv/direnvrc ]; then
+  source /run/current-system/sw/share/nix-direnv/direnvrc
+fi

README.md

@@ -14,9 +14,7 @@ $ ln -sv ~/.dotfiles/.hushlogin ~/
 $ ln -sv ~/.dotfiles/.gitignore ~/
 $ ln -sv ~/.dotfiles/.gitattributes ~/
 $ ln -sv ~/.dotfiles/.vimrc ~/.vimrc
-$ ln -sv ~/.dotfiles/darwin-configuration.nix ~/.nixpkgs/darwin-configuration.nix
-$ ln -sv ~/.dotfiles/.vimrc ~/.vimrc
-$ ln -sv ~/.dotfiles/direnvrc ~/.config/direnv/direnvrc
+$ ln -sv ~/.dotfiles/.direnvrc ~/.direnvrc
 $ ln -sv ~/.dotfiles/darwin-configuration.nix ~/.nixpkgs/darwin-configuration.nix
 $ mv ~/Library/Application\ Support/Sublime\ Text\ 3/Packages/User ~/Library/Application\ Support/Sublime\ Text\ 3/Packages/User.bak
 $ ln -sv ~/.dotfiles/sublime ~/Library/Application\ Support/Sublime\ Text\ 3/Packages/User

darwin-configuration.nix

@@ -2,7 +2,6 @@
 
 {
 
-
   # Used for backwards compatibility, please read the changelog before changing.
   # $ darwin-rebuild changelog
   system.stateVersion = 4;
@@ -75,6 +74,17 @@
     pkgs.vim
     pkgs.wget
     pkgs.youtube-dl
+    pkgs.nix-direnv
+  ];
+
+  # Support for https://github.com/nix-community/nix-direnv
+  # nix options for derivations to persist garbage collection
+  nix.extraOptions = ''
+    keep-outputs = true
+    keep-derivations = true
+  '';
+  environment.pathsToLink = [
+    "/share/nix-direnv"
   ];
 
 }

pins/nixpkgs.nix

@@ -1,5 +1,5 @@
 fetchTarball {
-  # https://github.com/NixOS/nixpkgs/tree/nixos-19.03 on 2020-05-10
-  url = "https://github.com/nixos/nixpkgs/archive/ab3adfe1c769c22b6629e59ea0ef88ec8ee4563f.tar.gz";
-  sha256 = "1m4wvrrcvif198ssqbdw897c8h84l0cy7q75lyfzdsz9khm1y2n1";
+  # https://github.com/NixOS/nixpkgs/tree/nixos-20.03 on 2020-08-08
+  url = "https://github.com/nixos/nixpkgs/archive/4364ff933ebec0ef856912b182f4f9272aa7f98f.tar.gz";
+  sha256 = "19ig1ywd2jq7qqzwpw6f1li90dq4kk3v0pbqgn6lzdabzf95bz6z";
 }

sublime/Preferences.sublime-settings

@@ -59,7 +59,8 @@
 		"schemas",
 		"niteoweb",
 		"Gunicorn",
-		"cachix"
+		"cachix",
+		"stylesheet"
 	],
 	"binary_file_patterns":
 	[
@@ -110,7 +111,6 @@
 		"nltk_data/",
 		"output/",
 		"parts/",
-		"poetry.lock",
 		"pip-selfcheck.json",
 		"selenium_screenshots/",
 		"share/",